In general, in a lawnmower, a cutter blade is made to rotate in a cutter housing, grass is cut by the cutter blade, and grass clippings are carried to a grass bag by air (carrier air) generated by the cutter blade.
After delivering the grass clippings to the grass bag, the carrier air passes through the grass bag and is discharged out from the grass bag. The carrier air causes noise and dust to be produced, and causes discomfort to the operator and people in the surrounding area.
A cover is attached to a peripheral edge of the grass bag in order to reduce dust. However, the carrier air is completely discharged from the grass bag, and discharged toward the area in which the operator is working. Attaching the cover is not a sufficiently effective countermeasure.
If the carrier air is returned to the cutter housing without being discharged from the grass bag, the total amount of the carrier air discharged from the grass bag will decrease. Such a system can effectively minimize dust.
Such an exhaust circulation lawnmower is known from U.S. Pat. No. 4,631,909 and Japanese Utility Model Laid-Open Publication No. 61-125223. In the exhaust circulation lawnmower, grass clippings are conveyed along with carrier air from a cutter housing to a grass bag, the grass clippings are left in the grass bag, and only the carrier air is recirculated to the cutter housing as exhaust.
Referring now to FIG. 8 hereof, discussion will be made as to the exhaust circulation lawnmower disclosed in U.S. Pat. No. 4,631,909.
An exhaust circulation lawnmower 200 shown in FIG. 8 comprises a cutter housing 201 that rotatably accommodates a cutter blade (not shown); a grass bag 202 that is provided to a rear of the cutter housing 201 and that stores the grass clippings; a grass clippings conveyance channel 203 that is provided to the cutter housing 201 and that is used to convey the grass clippings along with the carrier air from the cutter housing 201 to the grass bag 202; and an exhaust-recirculation channel 204 that is provided to the cutter housing 201 and that is used to recirculate the carrier air as exhaust from the grass bag 202 to the cutter housing 201 once the grass clippings have been held in the grass bag 202.
However, there is no mention of a ratio in the exhaust circulation lawnmower 200 between surface areas of a grass clippings discharge opening 205 that is provided to the grass bag 202 side of the grass clippings conveyance channel 203 and that is used to discharge, along with the carrier air, the grass clippings to the grass bag 202; and of a recirculation opening 206 that is provided to a grass bag 202 side of the exhaust-recirculation channel 204 and that is used to recirculate only the exhaust from the grass bag 202.
In other words, there exists a demand for a technique whereby, in an exhaust circulation lawnmower, when a grass clippings discharge opening is set to a predetermined size, a recirculation opening is provided for the carrier air at a size at which a predetermined capacity for grass clippings can be maintained without instances of the carrier air stopping in the grass clippings conveyance channel and grass bag.